I am a database administrator. Speaking purely from a DBA point of view, not from marketing or customer service, I would ask how long the company's database has to be bloated with records pertaining to people who do not fly the airline?
Dead people.
Retired people who never want to see the inside of any airplane ever again after 40 years of Road Warrior Life.
People who decide home and family are more important than cushy lounges, warm nuts and PDBs.
People with new jobs in new cities that don't ever fly this airline again.
People who say "Good Bye Cruel Airline" after some perceived insult and never fly this airline again.
There's gotta be some kind of cutoff, again speaking as a DBA. You don't have any activity at all for X amount of time, your records are dumped.